Patent GB-517524-A (GB)
Title: Improvements relating to fluid-blast electrical circuit interrupters
IPC: H01H33/70
Filed: 1938-07-20
Abstract: 517,524. Fluid-blast switches. BRITISH ELECTRICAL & ALLIED INDUSTRIES RESEARCH ASSOCIATION, WHITNEY, W. B., and SUMNER, W. July 20, 1938, No. 21592. [Class 38 (v)] A circuit-interrupter has relatively-movable arcing-electrodes arranged to separate within an arcing enclosure constituted by a movable casing surrounding the arc path. The casing throughout the first stage of electrode-separation has lostmotion with respect to one of the electrodes and is held in firm engagement with an abutment on the other, or on its mounting by the action of a magnetic field passing through magnetizable members secured to, or forming part of, the casing and the abutment respectively. Upon completion of the said first stage the casing and abutment are caused to separate and provision is made for automatically returning the former to its initial position when the breaker is being reclosed. The invention obviates the disadvantage of that of Specification 428,071, in that the casing cannot be forced prematurely away from its co-operating abutment by the high pressure set up by heavy current arcs. If the magnetic field is set up by the load current, its effect becomes greater the higher the pressure set up by that current and ceases when the arc is quenched. The field may, however, be set up by an external A.C. or D.C. source which may be disconnected automatically by an auxiliary switch after a time delay or by the breaker mechansim, or when the main current ceases. The drawing shows a load-current energized arrangement, in which a cylindrical fibre casing 1 slidably surrounding the movable contact 3, is urged upwards by a spring 24 bearing on an adjustable abutment 25. The fixed contact 5 comprises four segments with narrow gaps between and encircled by a spring 5a, the segments being secured by copper laminations 7 to a brass support 6 formed internally with four stops 10 which limit the upward movement of contact 3 in the closed position. The ring-like upper part of the support 6 is secured to the metal spider 8 by an insulating ring 9, whereas below it carries four lugs 11 providing seatings for two sets of laminations 12, 12a secured by bolts 13 and slotted at 14. A single-turn coil 15 is placed in the slot and has its ends connected to lugs secured to the support 6 and ring-like part of the spider, respectively, whereby the coil 15 is in series with the spider, support and contacts. Co-operating with the lower, pole, faces of 12, 12a are two sets of iron laminations serving as keepers and bolted to a brass block 19 having a ring-like part 20 secured to the casing 1. The laminations 12, 12a thus constitute the abutment for the casing 1. The blast set up by the arc during circuit-opening escapes upwardly through contact 5, and is deflected at 21 from the lead-in insulator, the blast being produced by oil or other liquid in the casing, or being of gaseous or other fluid from an external source or pump operated by the movable contact. Alternatively, a passage 22 in the latter may admit fluid under pressure to the arc through discharge-points 22a. To avoid chatter of the casing due to the passage of the current through zeroes of the cycle, a time-displaced flux may be set up by means of a short-circuited turn 26 in the laminations 12a adjacent casing 1. A modification is described which can best be understood by imagining the construction shown in Fig. 2 to be inverted and the functions of the contacts 3, 5 transposed by fixing 3 and moving 5 to open the circuit. The electromagnet may comprise a few turns wound within an annular fixed magnetic shell consisting of a pair of concentric cylinders, the gap at one end of which is closed. The casing on the movable contact carries a ring co-operating with the other end of the shell, there being overlap between the two to overcome the effect of the currentzeroes. The movable contact may be alternatively raised, or moved horizontally, to open circuit. The Provisional Specification states that the casing may be positively moved away in order to overcome effects of residual magnetism, and that the direction of any stray field in relation to that of the current is such as to move the arc, roots normally to the blast-direction. It also describes an arrangement in which the upper part of the casing has a number of superposed lateral vents, the top being closed except for the aperture which just admits the movable contact and a cylindrical insulating extension thereon.